A series of innovations over the past few years has resulted in an increase in the efficiency and power of linear laser diode arrays. It has become feasible to use the linear laser diode arrays as optical pump sources for neodymium doped solid state laser materials. A usual configuration of the laser diode array is in a monolithic bar shape of many individual emitters that are connected electrically in parallel and are essentially incoherent. Each emitter may be many tens or hundreds of microns wide but only a few microns high, and therefore the emission diverges strongly in a plane perpendicular to the bar with a typical full-width half-maximum of about 30 degrees. The polarization is parallel to the active plane (and bar).
Referring to FIG. 1, demonstrations have shown that when a laser diode array DA is close coupled or butted next to a laser rod barrel provided with a reflective coating RC to give relatively good pumping efficiency, for example, over 30% optical slope efficiency (defined as the derivative of laser energy out with pump energy) for Nd:YAG. This phenomenon is discussed at length in the article by Frank Hanson et al. entitled "Laser Diode Side Pumping of Neodymium Laser Rod" Applied Optics, Vol. 27, No. 1, 1 Jan. 1988. There is evidence to suggest that cylindrical focusing optics have been used to help collect more pump light and to image the array output inside of the laser rod.
Thus a continuing need exists in the state of the art for an improvement for a solid state laser rod pumped by linear laser diode arrays which increases the efficiency of such arrangements.